Add overscroll edge effect animations for Android.

content/browser/android/edge_effect.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/android/edge_effect.h"
+
+#include "cc/layers/layer.h"
+#include "ui/gfx/screen.h"
+
+namespace content {
+
+namespace {
+
+enum State {
+  STATE_IDLE = 0,
+  STATE_PULL,
+  STATE_ABSORB,
+  STATE_RECEDE,
+  STATE_PULL_DECAY
+};
+
+// Time it will take the effect to fully recede in ms
+const int kRecedeTime = 1000;
+
+// Time it will take before a pulled glow begins receding in ms
+const int kPullTime = 167;
+
+// Time it will take in ms for a pulled glow to decay before release
+const int kPullDecayTime = 1000;
+
+const float kMaxAlpha = 1.f;
+const float kHeldEdgeScaleY = .5f;
+
+const float kMaxGlowHeight = 4.f;
+
+// Note: The Android version computes the aspect ratio from the source texture;
+// because we use rescaled images, this is precomputed from the original Android
+// textures.
+const float kGlowImageAspectRatioInverse = 0.25f;
+
+const float kPullGlowBegin = 1.f;
+const float kPullEdgeBegin = 0.6f;
+
+// Minimum velocity that will be absorbed
+const float kMinVelocity = 100.f;
+
+const float kEpsilon = 0.001f;
+
+// How much dragging should effect the height of the edge image.
+// Number determined by user testing.
+const int kPullDistanceEdgeFactor = 7;
+
+// How much dragging should effect the height of the glow image.
+// Number determined by user testing.
+const int kPullDistanceGlowFactor = 7;
+const float kPullDistanceAlphaGlowFactor = 1.1f;
+
+const int kVelocityEdgeFactor = 8;
+const int kVelocityGlowFactor = 16;
+
+template <typename T>
+T Lerp(T a, T b, T t) {
+  return a + (b - a) * t;
+}
+
+template <typename T>
+T Clamp(T value, T low, T high) {
+   return value < low ? low : (value > high ? high : value);
+}
+
+template <typename T>
+T Damp(T input, T factor) {
+  T result;
+  if (factor == 1) {
+    result = 1 - (1 - input) * (1 - input);
+  } else {
+    result = 1 - std::pow(1 - input, 2 * factor);
+  }
+  return result;
+}
+
+gfx::Transform ComputeTransform(EdgeEffect::Edge edge,
+                                gfx::SizeF size, int height) {
+  switch (edge) {
+    default:
+    case EdgeEffect::EDGE_TOP:
+      return gfx::Transform(1, 0, 0, 1, 0, 0);
+    case EdgeEffect::EDGE_LEFT:
+      return gfx::Transform(0, 1, -1, 0,
+                            (-size.width() + height) / 2 ,
+                            (size.width() - height) / 2);
+    case EdgeEffect::EDGE_BOTTOM:
+      return gfx::Transform(-1, 0, 0, -1, 0, size.height() - height);
+    case EdgeEffect::EDGE_RIGHT:
+      return gfx::Transform(0, -1, 1, 0,
+                            (-size.width() - height) / 2 + size.height(),
+                            (size.width() - height) / 2);
+  };
+}
+
+void DisableLayer(cc::Layer* layer) {
+  DCHECK(layer);
+  layer->SetIsDrawable(false);
+  layer->SetTransform(gfx::Transform());
+  layer->SetOpacity(1.f);
+}
+
+void UpdateLayer(cc::Layer* layer,
+                 EdgeEffect::Edge edge,
+                 gfx::SizeF size,
+                 int height,
+                 float opacity) {
+  DCHECK(layer);
+  layer->SetIsDrawable(true);
+  layer->SetTransform(ComputeTransform(edge, size, height));
+  layer->SetBounds(gfx::Size(size.width(), height));
+  layer->SetOpacity(Clamp(opacity, 0.f, 1.f));
+}
+
+} // namespace
+
+EdgeEffect::EdgeEffect(scoped_refptr<cc::Layer> edge,
+                       scoped_refptr<cc::Layer> glow)
+  : edge_(edge)
+  , glow_(glow)
+  , edge_alpha_(0)
+  , edge_scale_y_(0)
+  , glow_alpha_(0)
+  , glow_scale_y_(0)
+  , edge_alpha_start_(0)
+  , edge_alpha_finish_(0)
+  , edge_scale_y_start_(0)
+  , edge_scale_y_finish_(0)
+  , glow_alpha_start_(0)
+  , glow_alpha_finish_(0)
+  , glow_scale_y_start_(0)
+  , glow_scale_y_finish_(0)
+  , state_(STATE_IDLE)
+  , pull_distance_(0)
+  , dpi_scale_(1) {
+  // Prevent the provided layers from drawing until the effect is activated.
+  DisableLayer(edge_);
+  DisableLayer(glow_);
+
+  dpi_scale_ =
+      gfx::Screen::GetNativeScreen()->GetPrimaryDisplay().device_scale_factor();
+}
+
+EdgeEffect::~EdgeEffect() { }
+
+bool EdgeEffect::IsFinished() const {
+  return state_ == STATE_IDLE;
+}
+
+void EdgeEffect::Finish() {
+  DisableLayer(edge_);
+  DisableLayer(glow_);
+  pull_distance_ = 0;
+  state_ = STATE_IDLE;
+}
+
+void EdgeEffect::Pull(base::TimeTicks current_time, float delta_distance) {
+  if (state_ == STATE_PULL_DECAY && current_time - start_time_ < duration_) {
+    return;
+  }
+  if (state_ != STATE_PULL) {
+    glow_scale_y_ = kPullGlowBegin;
+  }
+  state_ = STATE_PULL;
+
+  start_time_ = current_time;
+  duration_ = base::TimeDelta::FromMilliseconds(kPullTime);
+
+  delta_distance *= dpi_scale_;
+  float abs_delta_distance = std::abs(delta_distance);
+  pull_distance_ += delta_distance;
+  float distance = std::abs(pull_distance_);
+
+  edge_alpha_ = edge_alpha_start_ = Clamp(distance, kPullEdgeBegin, kMaxAlpha);
+  edge_scale_y_ = edge_scale_y_start_
+      = Clamp(distance * kPullDistanceEdgeFactor, kHeldEdgeScaleY, 1.f);
+
+  glow_alpha_ = glow_alpha_start_ =
+      std::min(kMaxAlpha,
+               glow_alpha_ + abs_delta_distance * kPullDistanceAlphaGlowFactor);
+
+  float glow_change = abs_delta_distance;
+  if (delta_distance > 0 && pull_distance_ < 0)
+    glow_change = -glow_change;
+  if (pull_distance_ == 0)
+    glow_scale_y_ = 0;
+
+  // Do not allow glow to get larger than kMaxGlowHeight.
+  glow_scale_y_ = glow_scale_y_start_ =
+      Clamp(glow_scale_y_ + glow_change * kPullDistanceGlowFactor,
+            0.f, kMaxGlowHeight);
+
+  edge_alpha_finish_ = edge_alpha_;
+  edge_scale_y_finish_ = edge_scale_y_;
+  glow_alpha_finish_ = glow_alpha_;
+  glow_scale_y_finish_ = glow_scale_y_;
+}
+
+void EdgeEffect::Release(base::TimeTicks current_time) {
+  pull_distance_ = 0;
+
+  if (state_ != STATE_PULL && state_ != STATE_PULL_DECAY)
+    return;
+
+  state_ = STATE_RECEDE;
+  edge_alpha_start_ = edge_alpha_;
+  edge_scale_y_start_ = edge_scale_y_;
+  glow_alpha_start_ = glow_alpha_;
+  glow_scale_y_start_ = glow_scale_y_;
+
+  edge_alpha_finish_ = 0.f;
+  edge_scale_y_finish_ = 0.f;
+  glow_alpha_finish_ = 0.f;
+  glow_scale_y_finish_ = 0.f;
+
+  start_time_ = current_time;
+  duration_ = base::TimeDelta::FromMilliseconds(kRecedeTime);
+}
+
+void EdgeEffect::Absorb(base::TimeTicks current_time, float velocity) {
+  state_ = STATE_ABSORB;
+  velocity = dpi_scale_ * std::max(kMinVelocity, std::abs(velocity));
+
+  start_time_ = current_time;
+  // This should never be less than 1 millisecond.
+  duration_ = base::TimeDelta::FromMilliseconds(0.1f + (velocity * 0.03f));
+
+  // The edge should always be at least partially visible, regardless
+  // of velocity.
+  edge_alpha_start_ = 0.f;
+  edge_scale_y_ = edge_scale_y_start_ = 0.f;
+  // The glow depends more on the velocity, and therefore starts out
+  // nearly invisible.
+  glow_alpha_start_ = 0.5f;
+  glow_scale_y_start_ = 0.f;
+
+  // Factor the velocity by 8. Testing on device shows this works best to
+  // reflect the strength of the user's scrolling.
+  edge_alpha_finish_ = Clamp(velocity * kVelocityEdgeFactor, 0.f, 1.f);
+  // Edge should never get larger than the size of its asset.
+  edge_scale_y_finish_ = Clamp(velocity * kVelocityEdgeFactor,
+                               kHeldEdgeScaleY, 1.f);
+
+  // Growth for the size of the glow should be quadratic to properly
+  // respond
+  // to a user's scrolling speed. The faster the scrolling speed, the more
+  // intense the effect should be for both the size and the saturation.
+  glow_scale_y_finish_ =
+      std::min(0.025f + (velocity * (velocity / 100) * 0.00015f), 1.75f);
+  // Alpha should change for the glow as well as size.
+  glow_alpha_finish_ =
+      Clamp(glow_alpha_start_,
+            velocity * kVelocityGlowFactor * .00001f, kMaxAlpha);
+}
+
+bool EdgeEffect::Update(base::TimeTicks current_time) {
+  if (IsFinished())
+    return false;
+
+  const double dt = (current_time - start_time_).InMilliseconds();
+  const double t = std::min(dt / duration_.InMilliseconds(), 1.);
+  const float interp = static_cast<float>(Damp(t, 1.));
+
+  edge_alpha_ = Lerp(edge_alpha_start_, edge_alpha_finish_, interp);
+  edge_scale_y_ = Lerp(edge_scale_y_start_, edge_scale_y_finish_, interp);
+  glow_alpha_ = Lerp(glow_alpha_start_, glow_alpha_finish_, interp);
+  glow_scale_y_ = Lerp(glow_scale_y_start_, glow_scale_y_finish_, interp);
+
+  if (t >= 1.f - kEpsilon) {
+    switch (state_) {
+      case STATE_ABSORB:
+        state_ = STATE_RECEDE;
+        start_time_ = current_time;
+        duration_ = base::TimeDelta::FromMilliseconds(kRecedeTime);
+
+        edge_alpha_start_ = edge_alpha_;
+        edge_scale_y_start_ = edge_scale_y_;
+        glow_alpha_start_ = glow_alpha_;
+        glow_scale_y_start_ = glow_scale_y_;
+
+        // After absorb, the glow and edge should fade to nothing.
+        edge_alpha_finish_ = 0.f;
+        edge_scale_y_finish_ = 0.f;
+        glow_alpha_finish_ = 0.f;
+        glow_scale_y_finish_ = 0.f;
+        break;
+      case STATE_PULL:
+        state_ = STATE_PULL_DECAY;
+        start_time_ = current_time;
+        duration_ = base::TimeDelta::FromMilliseconds(kPullDecayTime);
+
+        edge_alpha_start_ = edge_alpha_;
+        edge_scale_y_start_ = edge_scale_y_;
+        glow_alpha_start_ = glow_alpha_;
+        glow_scale_y_start_ = glow_scale_y_;
+
+        // After pull, the glow and edge should fade to nothing.
+        edge_alpha_finish_ = 0.f;
+        edge_scale_y_finish_ = 0.f;
+        glow_alpha_finish_ = 0.f;
+        glow_scale_y_finish_ = 0.f;
+        break;
+      case STATE_PULL_DECAY:
+        {
+          // When receding, we want edge to decrease more slowly
+          // than the glow.
+          float factor = glow_scale_y_finish_ != 0 ?
+              1 / (glow_scale_y_finish_ * glow_scale_y_finish_) :
+              std::numeric_limits<float>::max();
+          edge_scale_y_ = edge_scale_y_start_ +
+              (edge_scale_y_finish_ - edge_scale_y_start_) * interp * factor;
+          state_ = STATE_RECEDE;
+        }
+        break;
+      case STATE_RECEDE:
+        Finish();
+        break;
+      default:
+        break;
+    }
+  }
+
+  if (state_ == STATE_RECEDE && glow_scale_y_ <= 0 && edge_scale_y_ <= 0)
+    Finish();
+
+  return !IsFinished();
+}
+
+void EdgeEffect::ApplyToLayers(gfx::SizeF size, Edge edge) {
+  if (IsFinished())
+    return;
+
+  // An empty effect size, while meaningless, is also relatively harmless, and
+  // will simply prevent any drawing of the layers.
+  if (size.IsEmpty()) {
+    DisableLayer(edge_);
+    DisableLayer(glow_);
+    return;
+  }
+
+  float dummy_scale_x, dummy_scale_y;
+
+  // Glow
+  gfx::Size glow_image_bounds;
+  glow_->CalculateContentsScale(1.f, 1.f, 1.f, false,
+                                &dummy_scale_x, &dummy_scale_y,
+                                &glow_image_bounds);
+  const int glow_height = glow_image_bounds.height();
+  const int glow_bottom = static_cast<int>(std::min(
+      glow_height * glow_scale_y_ * kGlowImageAspectRatioInverse * 0.6f,
+      glow_height * kMaxGlowHeight) * dpi_scale_ + 0.5f);
+  UpdateLayer(glow_, edge, size, glow_bottom, glow_alpha_);
+
+  // Edge
+  gfx::Size edge_image_bounds;
+  edge_->CalculateContentsScale(1.f, 1.f, 1.f, false,
+                                &dummy_scale_x, &dummy_scale_y,
+                                &edge_image_bounds);
+  const int edge_height = edge_image_bounds.height();
+  const int edge_bottom = static_cast<int>(
+      edge_height * edge_scale_y_ * dpi_scale_);
+  UpdateLayer(edge_, edge, size, edge_bottom, edge_alpha_);
+}
+
+} // namespace content